Many companies are replacing metal parts with alternative materials that are lighter in weight but that are also capable of maintaining the structural benefits of metal. Due to the greater ease in processing plastic material into selected shapes, plastic materials have increased in popularity in terms of replacing metal parts. However, in many instances, plastic alone cannot match the strength properties of metals. As such, reinforced plastics or plastic composites have been utilized. Specifically, plastic composites include a reinforcing fiber in a polymer matrix. In many instances, the reinforcing fiber is glass fiber, although high-strength fibers such as aramid and carbon have been used in other applications.
The use of high glass loadings in thermoplastic materials tends to increase stiffness (tensile and flexural modulus) and strength (tensile & flexural strength) of the reinforced plastic. However, the use of highly glass filled materials has a negative effect on the surface quality and aesthetics of molded parts. After molding, the glass fibers on the exterior surface of the part produce a dull or matted finish and these fibers interfere with the adhesion of a subsequent painting or plating application that otherwise would cover the fibers.
Other types of filled or reinforced plastic materials suffer from similar problems. Traditional “high modulus” materials contain glass, or mica, or other fillers that are capable of increasing the modulus, or stiffness, of the material. Examples include glass filled PBT, PA, PC/ABS, PP, etc. However, the addition of fillers also has an adverse effect on the surface quality of the part. Therefore, these types of materials are molded in low gloss, textured applications. These parts can also be painted, but a primer is typically needed to cover the surface imperfections prior to the top-coat paint layer. As a result, “aesthetic” materials are typically unfilled, amorphous resins that can be easily molded-in-color, painted or metal plated. These materials include unfilled ASA, ABS, PC/ABS, PPO, etc. Again, however, these materials do not provide the structural strength necessary for many metal replacement applications.
Accordingly, it would be beneficial to provide a process for molding fiber-reinforced thermoplastic resins to produce an article having a resin-rich surface such that the presence of glass fibers and/or bundles on the external surface of the article are substantially eliminated. It would also be beneficial to provide a process for molding fiber-reinforced thermoplastic resins to produce an article capable of being plated. It would also be beneficial to provide an article molded from a fiber-reinforced thermoplastic resin wherein the resulting article were capable of being plated with a surface substantially free of visual defects.